A phase-locked loop (PLL), also referred to interchangeably herein as a frequency synthesizer, is a negative feedback system that locks a phase and frequency of a higher frequency device, usually a voltage controlled oscillator (VCO), whose phase and frequency are not very stable over temperature and time, to a more stable and lower frequency device, usually a temperature compensated or oven controlled crystal oscillator. A PLL is typically employed when there is a need for a high frequency local oscillator (LO) source. Example applications of PLLs are numerous and include wireless communications, medical devices, and instrumentation.